ASCE 7 Update and the Impact on Bolted Tanks

The latest edition of the American Society of Civil Engineering (ASCE) 7-16 Standard for Minimum Design Loads and Associated Criteria for Building and Other Structures published in August 2017, includes an exception to the AWWA D103.  Section relating to bolted steel tanks, includes new requirements regarding bolted tanks with an embedded steel base setting ring:

  • “b. For Type 6 tanks, the overturning ratio, J, as determined using AWWA D103, Eq. (14-32) shall not exceed 0.785.” This new verbiage has significance to bolted tank design as it impacts where a bolted tank with a Type 6 foundation can be used.

A Type 6 bolted steel tank utilizes a steel base ring shell embedded into the concrete foundation which also serves as the tank bottom.  The J ratio relates to the seismic loading and is a criteria used to determine if the storage tank requires anchorage.  A value of less than 0.785 indicates the tank wall will not experience uplift and does not need anchorage. Conversely, a J ratio greater than 1.54 requires the bolted tank to be mechanically anchored. Ratios between the two values may or may not require mechanical anchorage depending on other factors.


Essentially, the ASCE is requiring embedded shell bolted steel tanks not to be used in areas where uplift occurs due to seismic activity. The concern is there are no specific design requirements for  the anchorage of the shell to foundation and the concrete bottom included in the AWWA D103 therefore it is difficult to ensure ductility of the tank to foundation connection. There is a risk of the shell separating from concrete tank bottom during a seismic event as a design criteria does not exist to ensure the connection is properly designed. ASCE 7-16 does not restrict bolted tanks with other foundation types; only tanks with an embedded shell.


For most applications, Superior Tank Co., Inc. will design our bolted tanks to use foundation types 1 through 5. With foundation types 1 through 5, the storage tank will include a steel bottom which structurally ties into the bolted tank shell creating one uniform structure.


This new terminology is another example of how bolted tank standards are continuously evolving resulting in more resilient bolted steel tanks.

NSF International Certification for Bolted Tanks

NSF Storage Tanks

Superior Tank Company is proud to announce we have recently earned NSF International Certification for our bolted steel tanks over 14,309 gallons. NSF/ANSI 61 and 372 Certification of our bolted tanks demonstrates compliance to the internationally recognized health effects standard for drinking water system components. NSF International led the development of the American National Standards for all materials and products coming into contact with drinking water and NSF/ANSI 61 & 372 sets health effects criteria for many water system products, components and materials. For example, NSF International standards are used to verify the safety and performance of water treatment and plumbing components and to ensure these products do not leach harmful levels of contaminants into drinking water.

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How Much Does A Bolted Steel Tank Cost?

33 Years of Bolted Tanks

One of the first questions we are asked is “how much does a bolted steel tank cost”? Unfortunately, the answer is a little complex as the price of a bolted tank is impacted by a variety of factors. Elements include storage tank design specification, relevant local building codes, quality of raw materials, scope of work included in the contract, manufacturer experience and tank installation team skills/training.

The various design specifications such as AWWA D103, NFPA 22 and API 12B determine tank appurtenances, shell design, steel thickness and even tank size in some cases. For example, the American Water Works Association (AWWA) D103 standard applies to all bolted tanks used for potable water storage and mandates the interior epoxy coating is NSF 61 certified. Bolted tanks for fire protection need to comply with the National Fire Protection Association (NFPA) 22 standards which requires specific tank components such as tank heating systems when needed and reinforced concrete ringwall foundation. When a bolted tank is used for oil storage, the American Petroleum Institute (API) 12B standard is commonly used as a reference but tanks do not have to comply. However, for customers desiring a guaranteed level of quality, the API 12B monogram program ensures the tank meets very specific design criteria and the bolted tank manufacturer is API Spec Q1 / ISO 9001:2008 certified.

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Over 33 YEARS of Building Bolted Steel Tanks!

33 Years of Bolted Tanks

Superior Tank Co., Inc. (STCI) has been engineering, manufacturing and installing bolted steel tanks since 1984. Over the last 33 years, STCI has manufactured thousands of bolted tanks which have been successfully installed throughout the world.

Our history has shown STCI has the strength and structure to last. STCI is one of the few bolted tank manufacturers in the United States and the only company which is family owned and operated providing our customers with the confidence that they are purchasing from a company with the highest values and standards. As we operate our own State-of-the-Art bolted tank manufacturing plant and welded steel tank fabrication facility, we have complete control of our quality and tank production schedule. Our bolted steel tank production facilities also include a powder coating line allowing us to offer various powder coating formulas including epoxy and TGIC polyester as well as specialized Scotchkote for extremely corrosive liquids.

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How Seismic Use Group Classification affects your Water Storage Tank

Seismic Use Group Bolted Tank

When purchasing a bolted steel tank or a welded steel water storage tank, one of the key criteria determining the design parameters of the tank is the Seismic Use Group (SUG) classification. The term Seismic Use Group is essentially the same as the terms Occupancy Category and Risk Category used by the International Building Code (IBC) and the American Society of Civil Engineers (ASCE). The Seismic Use Group classification is used to determine the magnitude of environmental loading applied to the bolted or welded tank structure. Despite the name, the Seismic Use Group classification is applicable to other environmental loads such as wind, snow, ice, and floods.

The Seismic Use Group along with the seismic accelerations at the site help determine the Seismic Design Category of a structure. Seismic Design Category is a letter rating from A to F with F being the worst case. There are special detailing requirements depending on what Seismic Design Category a structure is in. For example, with steel water storage tanks, the seismic design category impacts how the anchor bolts are designed.


Superior Tank Installs Innovative Bolted Tank

Superior Tank Co., Inc. (STCI) is proud to have provided the new bolted steel tank for the Cauayan City Water District in Isabela Philippines. The bolted tank is the first of its kind in Northern Luzon and highlights the benefits of a bolted steel tank. The epoxy coated tank provides storage of 79,000 gallons of potable water for Cauayan City and is dedicated to the late Governor Faustino N. Dy and his son Governor Benjamin G. Dy. Their vision and initiatives have resulted in the development and modernization of the Cauayan City Water District and also contributed to the City being branded as “Ideal City of The North”.

The bolted steel tank used for the project was designed and manufactured to provide the city decades of service. Constructed of high strength carbon steel, the bolted tank is constructed for maximum durability and longevity. To meet local building codes and to withstand typhoons, the bolted tank is designed to meet a 200 mph wind load requirement.  To accommodate the city’s future needs and save the city time and money, the bolted tank was designed to be easily expandable by simply adding rings to the tank.  To survive the warm and humid conditions of the Philippines, the epoxy bolted tank features a corrosive resistant powder coating with an additional Silica-Zirconium(Si-Zr) underseal. To resist the harsh sun and UV rays, the exterior of the bolted tank was protected with specially formulated TGIC powder coating.  Our Sky White color was selected to reduce the solar heat gain which helps to keep the water cooler and preserve water quality.  In addition, bolted tanks manufactured by STCI are different than bolted tanks from other companies as it includes a steel floor.  The steel floor ties the shell together and prevents leaks and water loss which can occur with concrete bottom tanks.

The bolted steel tank in Cauayan City is truly an investment in the community and a testament to the vision of Governor Faustino N. Dy and Governor Benjamin G. Dy.

Contact us to learn how we can help you plan for the future!

Complete Solutions for Oil Storage Tanks

Bolted Oil Storage Tank

For over 30 years, Superior Tank Co., Inc. (STCI) has designed, manufactured, installed and serviced bolted tanks and welded tanks for oil storage. STCI is one of the only bolted steel manufacturers which can proudly display the prestigious American Petroleum Institute (API) SPEC 12B monogram on our bolted tanks for oil storage. In order for a bolted tank to include the API 12B monogram, the storage tank must strictly adhere to the API SPEC 12B standards. In addition, the tank manufacturer must be recertified on an annual basis to meet the strict API SPEC Q1/ISO 9001:2008 quality standards.

All STCI bolted tanks for oil storage are engineered and manufactured to meet the strict API SPEC 12B design standard and include numerous elements to increase tank durability and longevity. To seal our tanks, we use heavy duty gaskets made of Buna-N or Viton in place of mastic putty which is incompatible with oil storage. Our custom made Buna-N and Viton gaskets are extremely durable and resistant to crude oil and other corrosive liquids. Also, to increase the lifespan of the bolted tank, our gaskets have high tensile strength to prevent tearing and remain flexible over time. In addition, our gaskets do not require routine replacement thereby decreasing maintenance requirements. To reduce service intervals, our bolted tanks feature premium Scotchkote powder coating which is specifically formulated for oil storage. Our API SPEC 12B bolted tanks range in capacity from 100 to 10,000 bbls and adhere to dimensions determined by the API SPEC 12B specification. Read More “Complete Solutions for Oil Storage Tanks”

What makes a bolted tank “Superior”?

Various companies sell bolted steel tanks, but there is only one “Superior Tank”. Is there really a difference between bolted tanks manufactured by Superior Tank Co., Inc. (STCI) and bolted steel tanks and glass-lined bolted steel tanks made by other companies? The answer is in short “yes” for various reasons including STCI’s precise manufacturing processes, premium raw materials, extensive company history, API SPEC Q1 / ISO 9001:2008 certification and outstanding customer service. Superior Tank Co., Inc. is one of the few bolted tank manufacturers in the United States and the only bolted tank company with manufacturing facilities in both California and Texas. Owning and operating State-of-the-Art manufacturing facilities gives STCI complete control of the quality of our bolted tanks and we are not reliant on outside companies for the quality of our bolted steel storage tanks. All of our bolted tanks use quality materials such as heavy duty Grade 5 or Grade 8 high tensile strength bolts and the steel used for our bolted tanks is verified to meet specific quality standards such as surface quality, edge quality, silicone content, squaredness and flatness. In addition, our specially formulated powder coating and corrosion preventing SiZr seal maximize the lifespan of the epoxy coating of the bolted tank. Our heavy duty gaskets ensure our bolted tanks remain in service and do not require storage tanks to be taken offline to replace the mastic which is used with glass-fused-to-steel bolted tanks. We have invested heavily in precision equipment such as CNC machinery, Automated Robotic Technology (ART), and advanced turret punches to ensure our bolted steel tanks are manufactured with exacting precision. As our bolted steel tanks are crafted with such accuracy, components fit together perfectly, eliminating tank leaks and field rework. To confirm our bolted tanks meet or exceed quality standards, STCI has implemented various Quality Management Systems and is API SPEC Q1 / ISO 9001:2008 certified. Various processes and procedures have been put into place to ensure our bolted steel tanks meet customer expectations and delivery schedule. In addition, STCI has earned the reputation of providing exceptional customer service and ensuring our customers are happy with their new epoxy coated bolted tank. The results of these extra efforts are illustrated in our excellent Customer Satisfaction rating and customer testimonials. When all of these factors are considered, it is evident what makes our tanks, “Superior”.

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Fire Protection Storage Done Right

Water storage tanks for fire protection has improved in recent years as technology has advanced, processes have evolved and standards have become more rigorous resulting in increased flexibility, greater durability and lower costs.

Modern ground storage tanks used for fire protection are commonly one of three designs; bolted steel tanks, welded steel tanks and concrete tanks. Concrete tanks are commonly used for projects requiring greater than 80,000 gallons of water storage due to the high set up cost of the required equipment on the job site. This expense makes smaller concrete tanks cost prohibitive relative to other designs. Welded steel tanks for fire protection provide a wider range of capacities anywhere between 25,000 to 3,500,000 gallons. In addition, welded steel tanks are available in a variety of configurations including reservoir style storage tanks and standpipe water tanks. For certain applications, customers prefer the smooth exterior of a welded steel storage tank.

Of the three types of ground storage tanks, bolted steel tanks provides the greatest flexibility, outstanding longevity and best cost efficiency. Bolted tanks provide the larger range of sizes, from 5,000 to 3,500,000 gallons. For most fire protection projects, the storage tanks required range in capacity from 25,000 to 250,000 gallons which is well suited for a bolted steel tank. Bolted steel tanks are frequently used within existing infrastructure to increase water storage or to provide storage in remote areas. For example, when a new warehouse is built and requires water for fire protection, a new bolted steel tank can easily be installed on site, even in areas with constrained space. Alternatively, bolted tanks work well for remote areas and are available in either closed-top or open-top “scoop tank” design. Read More “Fire Protection Storage Done Right”

We Don’t Crack Under Pressure!

We Don't Crack Under Pressure! (glass)

In the bolted steel tank industry, two coating options are common; factory powder coating and glass-fused-to-steel coating. Each of the coatings has its own unique properties and characteristics when applied to bolted tanks and steel tanks for water storage.

Bolted tanks with a glass-fused-to-steel coating are attractive to potential buyers as the coating is non-porous and very rigid. The glass is applied directly to the steel then heated to 1500˚F to melt the glass and bond the glass to the steel. In theory, the glass coating isolates the steel from the liquids stored in the bolted tank. Unfortunately, the real world can be very different from theory. Ironically, the same properties which make the glass coating attractive for use with water storage tanks also make the coating vulnerable to cracking. The rigidity of the coating does not allow the glass to flex with the steel tank panels which expand and contract with temperature changes. This difference in expansion rates can lead to the coating cracking under stress. In addition, the extreme rigidity of the glass coating can help to resist very minor impacts but can lead to cracking if impacted with any significant force. When the coating on a glass-lined bolted tank cracks, the steel underneath is exposed and corrosion will likely occur. After the corrosion starts to spread, it can result in undercutting and the overall failure of the coating. As the glass coating is applied to the steel at the factory and melted at a very high temperature, it is not possible to fully repair a bolted tank with a glass-fused-to-steel coating. The only “fix” possible is to cover the cracked area with mastic. The proper way to ensure the panel does not experience corrosion and coating failure is to replace the entire damaged panel as glass-lining cannot be fixed or repaired in the field. The vulnerability of a glass-lined tank to impact makes it critical to protect the storage tank panels during shipping and installation as well as after the ground storage tank is installed. A dropped tool or thrown rock can result in an expensive repair and require the storage tank to be taken out of service to replace an entire panel.

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